1. Field of the Invention
The construction of the cable consists in applying swellable threads and/or powders around the dielectric central reinforcement. Afterwards, the tubes containing the optical fiber are laid around the above mentioned central reinforcement, followed by the application of swellable tapes enveloping the assembly forming in this way the core of the cable. Then, swellable aramide fiber or swellable fiber glass, a first plastic cover, a metal armature, or the final cover can be laid, inserting always between each additional element a swellable tape. This tape will contribute to prevent humidity penetration between the various layers protecting the core of the cable depending on the use, either aerial or underground.
2. Description of the Prior Art
Currently, various cables are known on the international market that meet the growing demand for communication of speech, video and data. These cables have revolutionized telecommunications offering services that facilitate the development of intercommunications because of their high quality, high conduction capacity and high transmission speed.
Among these various cables, the ones used in what is known as outside or exterior plant, because they are exposed to weathering, have to be manufactured to withstand different environment conditions, such as temperature changes and humidity.
To avoid the penetration of humidity, several compounds are typically known that are in the form of jellies that are used both inside and outside the tubes containing the optical fiber (loosely fitting tubes). These compounds are presented in U.S. Pat. No. 5,999,677 which discloses an improved optical fiber cable in which the importance of protecting the optical fiber against humidity is discussed.
The use of said jellies causes some inconveniences which are evident in design, process and installation limitations of optical fiber cables for outside use. With regard to design, they limit the types of materials that can be used for the manufacturing of the tube as well as the other components of the cable since they must be chemically compatible to avoid degradation and consequent damage to the optical fibers. With regard to the manufacturing process, special equipment is required to impregnate the cable with jelly and to control its application which is time consuming, dirty and complicated. With regard to cable installation, to perform terminal connections or splicing, the ends of the cable have to be prepared, cleaning each one of the components until the jelly is eliminated and connections can be made. This implies the use of solvents for cleaning purposes, but said materials degrade the tube containing the optical fiber cable or the protecting covers of the cable. On the other hand, because this operation is time consuming and dirty, it can cause slight skin and airway irritations to the people installing the cables if they do not wear adequate protections and take appropriate precautions.
One of the main characteristics that the optical fiber cable have to fulfill, in the case of installations known as external or exterior plant cables, is that the fibers be duly protected against possible contact with humidity. This contact causes the formation of hydrogen, which attacks the fibers, affecting their performance and life. For this reason, the cables must be manufactured in such a way that their integrity is ensured (if they are properly made during the manufacturing process itself). During the installation process and in operation, humidity penetration inside the cable must be prevented; otherwise, hydrogen would form and optical fibers would be damaged.
For this reason, two types of protection are known. The most commonly used consists of protecting the fibers inside and the tube outside containing them and between the different armatures and covers that constitute the cable with a jelly forming an impenetrable barrer to humidity. The second type of protection makes use of tapes and powders absorbing humidity to offer the same protective effect for the fibers.
In U.S. Pat. No. 5,082,719, a communication cable is described, the characteristic of which is that it prevents water from penetrating inside the cable by means of a tape impregnated with superabsorbent material placed between the core and the jacket and enveloping the core longitudinally. Upon contact with water, the superabsorbent material swells and impedes water penetration.
In U.S. Pat. No. 4,909,592, a communication cable is described which presents elements to block water penetration in the core located in a tube and a cover system. Said elements can be tapes or threads or both, with superabsorbent materials.